High‐Sensitivity Determination of Lead(II) and Cadmium(II) Based on the CNTs‐PSS/Bi Composite Film Electrode

A high‐sensitivity sensing platform for lead(II) and cadmium(II) based on the bismuth modified carbon nanotubes (CNTs)‐poly(sodium 4‐styrenesulfonate) composite film electrode (CNTs‐PSS/Bi) was fabricated. The composite film CNTs‐PSS/Bi provided remarkably improved sensitivity and reproducibility compared with previously reported CNTs‐modified electrodes. The detection limits were estimated to be 0.04 ppb for lead(II) and 0.02 ppb for cadmium(II) with a preconcentration time of 120 s, respectively. The linear responses of Cd²⁺ and Pb²⁺ were over the ranges of 0.5–50 ppb and 0.5–90 ppb, respectively. Finally, the practical application of the proposed method was verified in the real water sample with satisfactory results.     

纳米碳管电极的制备与电化学检测性能研究

纳米碳管由于其独特的物理和化学性能及广阔的应用前景而备受关注,其相关研究涉及到众多领域[1￣3]。在电化学分析领域,与其它碳电极材料相比,纳米碳管电极具有较大的电极表面积和较高的电子传递速率,其使用能增大响应电流、降低检出限,是目前电化学分析电极中一个十分引人注目     

Detection of Trace Heavy Metal Ions Using Carbon Nanotube‐ Modified Electrodes

A sensitive voltammetric method for detection of trace heavy metal ions using chemically modified carbon nanotubes (CNTs) electrode surfaces is described. The CNTs were covalently modified with cysteine prior to casting on electrode surfaces. Cysteine is an amino acid with high affinities towards some heavy metals. In this assay, heavy metals ions accumulated on the cysteine‐modified CNT electrode surfaces prior to being subjected to differential pulse anodic stripping voltammetry analysis. The resulting peak currents were linearly related to the concentrations of the metal ions. The method was optimized with respect to accumulation time, reduction time and reduction potential. The detection limits were found to be 1 ppb and 15 ppb for Pb²⁺ and Cu²⁺ respectively. The technique was used for the detection of Pb²⁺ and Cu²⁺ in spiked lake water. The average recoveries of Pb²⁺ and Cu²⁺ were 96.2% and 94.5% with relative standard deviations of 8.43% and 7.53% respectively. The potential for simultaneous detection of heavy metal ions by the modified CNTs was also demonstrated.     

ABTS‐Multiwalled Carbon Nanotubes Nanocomposite/Bi Film Electrode for Sensitive Determination of Cd and Pb by Differential Pulse Stripping Voltammetry

A 2,2′‐azinobis (3‐ethylbenzothiazoline‐6‐sulfonate) diammonium salt (ABTS)‐multiwalled carbon nanotubes (MWCNTs) nanocomposite/Bi film modified glassy carbon (GC) electrode was constructed for the differential pulse stripping voltammetric determination of trace Pb²⁺ and Cd²⁺. This electrode was more sensitive than ABTS‐free Bi/GC and Bi/MWCNTs/GC electrodes. Linear responses were obtained in the range from 0.5 to 35 μg L^?1 for Cd²⁺ and 0.2 to 50 μg L^?1 Pb(II), with detection limits of 0.2 μg L^?1 for Cd²⁺ and 0.1 μg L^?1 for Pb²⁺, respectively. This sensor was applied to the simultaneous detection of Cd²⁺ and Pb²⁺ in water samples with satisfactory recovery.     

A NADH Sensor Based on 1,2‐Naphththoquinone Electropolymerized on Multi‐walled Carbon Nanotubes Modified Glassy Carbon Electrode

A new carbon nanotubes modified electrode (poly‐Nq‐MWCNTs/GCE) was fabricated by electropolymerization of 1,2‐naphththoquinone to the surface of multi‐walled carbon nanotubes modified electrode by casting method. The morphology of the nanocomposite was characterized by scanning electron microscopy. Cyclic voltammetry and chronoamperometry were applied to investigate the electrochemical properties of the poly‐Nq‐MWCNTs nanocomposite modified electrode. The result of electrochemical experiments showed that such modified electrode had a favorable catalytic ability to oxidation of β‐nicotinamide adenine dinucleotide (NADH). The resulted sensor was sensitiveness to NADH and achieved 95β of the steady‐state current within 5s. Furthermore, the anodic peak current was linear to the concentration of NADH for the range from 1.0 μM to 0.14 mM. The linear equation was: I(μA) = 0.3987 + 0.1035c (μmol/L), the correlation coefficient r = 0.9962, the detect limit is down to 1 × 10^?7 M (S/N = 3) and the sensitivity is 0.1035 μA/mmol. The well catalytic activity of the sensor was ascribed to the synergistic effect role played by MWCNTs and poly‐Nq. Moreover, the based sensor possesses good stability and reproducibility.     

Electrochemical Determination of Copper(II) in Water Samples Using a Novel Ion-Selective Electrode Based on a Graphite Oxide–Imprinted Polymer Composite

A novel copper(II)-selective electrode based on graphite oxide/imprinted polymer composite was developed for the electrochemical monitoring of copper(II) (Cu²⁺) ions. The electrode exhibited highly selective potentiometric response to Cu²⁺ with respect to common alkaline, alkaline earth and heavy metal cations. The composite composition studies indicated that the most suitable composite composition performing the most promising potentiometric properties was 20.0% ionophore (Cu²⁺-ion imprinted polymer), 10.0% paraffin oil, 5.0% multiwalled carbon nanotubes, and 65.0% graphite oxide. The fabricated electrode exhibited a linear response to Cu²⁺ over the concentration range of 1.0?×?10^??6–1.0?×?10^??1?M (correlation coefficient of 0.9998) with a sensitivity of 26.1?±?0.9?mV decade^??1. The detection limit of the fabricated electrode was determined to be 4.0?×?10^??7?M. The electrode worked well in the pH range of 4.0–8.0. The electrode had stable, reversible and fast potentiometric response (3?s). In addition, the electrode had a lifetime of more than 1 year. The analytical applications of the proposed electrode were performed using as an indicator electrode for the potentiometric titration of Cu²⁺ with ethylene diamine tetraacetic acid solution and for the determination of Cu²⁺ of spiked river, dam, and tap water samples. The obtained results for potentiometric titration and water samples were satisfactory.     

A Potentiometric Sensor for Cd2+ Based on Carbon Nanotube Paste Electrode Constructed from Room Temperature Ionic Liquid,Ionophore and Silica Nanoparticles

A novel and effective potentiometric sensor for the rapid determination of Cd²⁺ based on carbon paste electrode consisting of the room temperature ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate, multiwalled carbon nanotubes, silica nanoparticles and ionophore was constructed. The prepared composite has a low potential drift, high selectivity and fast response time, which leads to a more stable potential signal. A linear dynamic range of 4.50×10^?9–1.00×10^?1 mol L^?1 with a detection limit of 2.00×10^?9 mol L^?1 was obtained. The modified electrode was successfully applied to the accurate determination of trace amounts of Cd²⁺ in environmental and biological samples.     

Bismuth/Polyaniline/Glassy Carbon Electrodes Prepared with Different Protocols for Stripping Voltammetric Determination of Trace Cd and Pb in Solutions Having Surfactants

To improve reproducibility, stability and sensitivity, a bismuth (Bi) thin film was coated on glassy carbon (GC) substrates which surfaces were modified with a porous thin layer of polyaniline (PANI) via multipulse potentiostatic electropolymerization to form Bi/PANI/GC electrodes (Bi/PANI/GCEs). The Bi/PANI/GCEs were used successfully for simultaneous detection and determination of Cd²⁺ and Pb²⁺ ions, and various parameters were studied with reference to square wave anodic stripping voltammetric (SWASV) signals. The experimental results depicted that the environment‐friendly Bi/PANI/GCEs had the ability to rapidly monitor trace heavy metals even in the presence of surface‐active compounds.     

Zinc oxide nanostructured platform for electrochemical detection of heavy metals

ZnO nanoparticles (ZnO-NP) were prepared by a facile precipitation technique using di-isopropyl amine as precipitating agent. The morpho-structure and porosity of the as-prepared nano-powder were investigated by FT-IR analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET analysis. By drop-casting, a composite film was deposited to obtain ZnO-NP-Nafion/GCE modified electrode. The modified electrode was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and square wave anodic stripping voltammetry (SWASV) for the detection of Pb²⁺, Cd²⁺, Cu²⁺, and Fe³⁺, and it was successfully applied for the detection of Pb²⁺ and Cu²⁺ in real water samples.     

A Self‐assembled L‐Cysteine and Electrodeposited Gold Nanoparticles‐reduced Graphene Oxide Modified Electrode for Adsorptive Stripping Determination of Copper

Glassy carbon electrode (GCE) modified with L‐cysteine and gold nanoparticles‐reduced graphene oxide (AuNPs‐RGO) composite was fabricated as a novel electrochemical sensor for the determination of Cu²⁺. The AuNPs‐RGO composite was formed on GCE surface by electrodeposition. The L‐cysteine was decorated on AuNPs by self‐assembly. Physicochemical and electrochemical properties of L‐cysteine/AuNPs‐RGO/GCE were characterized by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, Raman spectroscopy, X‐ray diffraction, cyclic voltammetry and adsorptive stripping voltammetry. The results validated that the prepared electrode had many attractive features, such as large electroactive area, good electrical conductivity and high sensitivity. Experimental conditions, including electrodeposition cycle, self‐assembly time, electrolyte pH and preconcentration time were studied and optimized. Stripping signals obtained from L‐cysteine/AuNPs‐RGO/GCE exhibited good linear relationship with Cu²⁺ concentrations in the range from 2 to 60 μg L⁻¹, with a detection limit of 0.037 μg L⁻¹. Finally, the prepared electrode was applied for the determination of Cu²⁺ in soil samples, and the results were in agreement with those obtained by inductively coupled plasma mass spectrometry.     

Carbon Nanotubes/Ionophore Modified Electrode for Anodic Stripping Determination of Lead

Bifunctional combination of carbon nanotubes and ionophore is introduced for anodic stripping analysis of lead (Pb²⁺). Carbon nanotubes are employed to improve the detection sensitivity due to their excellent electrical conductivity and strong adsorption ability. An ionophore is utilized for its excellent selectivity toward Pb²⁺. The proposed carbon nanotubes/ionophore modified electrode shows improved sensitivity and selectivity for Pb²⁺. Low detection limit (1 nM), wide linear range (5 nM–8 µM) and excellent selectivity over other metal ions (Cd²⁺, Cu²⁺, and Hg²⁺) was obtained. The practical application has been carried out for determination of Pb²⁺ in real water samples.     

Ordered Mesoporous Carbon and Thiolated Polyaniline Modified Electrode for Simultaneous Determination of Cadmium(II) and Lead(II) by Anodic Stripping Voltammetry

The fabrication and evaluation of a glassy carbon electrode (GCE) modified with ordered mesoporous carbon (OMC), 2‐mercaptoethanesulfonate (MES)‐tethered polyaniline (PANI) and bismuth for simultaneous determination of trace Cd²⁺ and Pb²⁺ by differential pulse anodic stripping voltammetry (DPASV) are presented here. The morphology and electrochemical properties of the fabricated electrode were respectively characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Experimental parameters such as PANI disposition, preconcentration potential, preconcentration time and bismuth concentration were optimized. Under optimum conditions, the fabricated electrode exhibited linear calibration curves ranged from 1 to 120 nM for Cd²⁺ and Pb²⁺. The limits of detection (LOD) were 0.26 nM for Cd²⁺ and 0.16 nM for Pb²⁺ (S/N=3), respectively. Additionally, repeatability, reproducibility, interference and application were also investigated, and the proposed electrode exhibited excellent performance. The proposed method could be extended for the development of other new sensors for heavy metal determination.     

Surface Modification of Gold by Quercetin Monolayer for the Electrochemical Determination of Copper(II)

A quercetin monolayer has been prepared on top of the self‐assembled 3‐mercaptopropionic acid (MPA) layer for the copper ion determination. Cu²⁺ ions are readily accumulated on this modified electrode through the complex formation and electrochemically detected. With a quercetin layer, the redox process of Cu²⁺ became more reversible than at the MPA‐modified electrode. Complexation sites in MPA and quercetin were occupied within five min when the electrode was immersed in 10 μM Cu²⁺ solution. The MPA and quercetin layers were stable enough to allow repeated EDTA treatment to remove adsorbed Cu²⁺ for the surface regeneration. Only 7% decrease was found after ten times regeneration and use. Linear current response was found over the concentration range of 1 nM and 10 μM with detection limit of 0.1 nM. Common interfering ions such as Cd²⁺, Zn²⁺, and Fe^2+/3+ did not show any electrochemical response in the potential range of Cu²⁺ determination.     

Reversible Electrochemical Modulation of a Catalytic Nanosystem

A catalytic system based on monolayer‐functionalized gold nanoparticles (Au NPs) that can be electrochemically modulated and reversibly activated is reported. The catalytic activity relies on the presence of metal ions (Cd²⁺ and Cu²⁺), which can be complexed by the nanoparticle‐bound monolayer. This activates the system towards the catalytic cleavage of 2‐hydroxypropyl‐p‐nitrophenyl phosphate (HPNPP), which can be monitored by UV/Vis spectroscopy. It is shown that Cu²⁺ metal ions can be delivered to the system by applying an oxidative potential to an electrode on which Cu⁰ was deposited. By exploiting the different affinity of Cd²⁺ and Cu²⁺ ions for the monolayer, it was also possible to upregulate the catalytic activity after releasing Cu²⁺ from an electrode into a solution containing Cd²⁺. Finally, it is shown that the activity of this supramolecular nanosystem can be reversibly switched on or off by oxidizing/reducing Cu/Cu²⁺ ions under controlled conditions.     

Electrocatalytic Oxidation of Dopamine at a Nanocuprous Oxide‐Methylene Blue Composite Glassy Carbon Electrode

Cuprous oxide nanowhisker was prepared by using cetyltrimethyl ammonium bromide (CATB) as soft template, and was characterized by XRD and TEM methods. The electrochemical properties of nano‐Cu₂O and nano‐Cu₂O‐methylene blue (MB) modified electrode were studied. The experimental results indicate that nano‐Cu₂O shows a couple of redox peaks corresponding to the redox of Cu(II)/Cu(I), the peak currents are linear to the scan rates which demonstrate that the electrochemical response of Cu₂O is surface‐controlled. The composite nano‐Cu₂O‐Nafion‐MB modified electrode shows a trend of decrease of peak currents corresponding to the Cu (II)/Cu (I). However, the electrocatalytic ability of nano‐Cu₂O‐MB composite film to dopamine increases dramatically. At this composite electrode, dopamine shows a couple of quasireversible redox peaks with a peak separation of 106 mV, the peak current increases about 8 times and the oxidation peak potential decreases about 200 mV as compared to that at bare glassy carbon electrode. The peak currents change linearly with concentration of dopamine from 1×10^?7 to 3.2×10^?4 mol/L, the detection limit is 4.6×10^?8 mol/L. The composite electrode can effectively eliminate the interference of ascorbic acid and has better stability and excellent reproducibility.     

Electrochemical sensor for Cd2+ and Pb2+ detection based on nano-porous pseudo carbon paste electrode

An electrochemical sensor based on self-made nano-porous pseudo carbon paste electrode (nano-PPCPE) has been successfully developed, and used to detect Cd²⁺ and Pb²⁺. The experimental results showed that the electrochemical performance of nanoPPCPE is evidently better than both glassy carbon electrode (GCE) and pure carbon paste electrode (CPE). Then the prepared nano-PPCPE was applied to detect Cd²⁺ and Pb²⁺ in standard solution, the results showed that the electrodes can quantitatively detect trace Cd²⁺ and Pb²⁺, which has great significance in electrochemical analysis and detection. The linear ranges between the target ions concentration and the DPASV current were from 0.1–3.0 μmol/L, 0.05–4.0 μmol/L for Cd²⁺ and Pb²⁺, respectively. And the detection limits were 0.0780 μmol/L and 0.0292 μmol/L, respectively. Moreover, the preparation of the nano-PPCPE is cheap, simple and has important practical value.     

Trace Analysis of Heavy Metals (Cd,Pb, Hg) Using Native and Modified 3D Printed Graphene/Poly(Lactic Acid) Composite Electrodes

Here we investigate the use of 3D printed graphene/poly(lactic acid) (PLA) electrodes for quantifying trace amounts of Hg, Pb, and Cd. We prepared cylindrical electrodes by sealing a 600 μm diameter graphene/PLA filament in a pipette tip filled with epoxy. We characterized the electrodes using scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry in ferrocene methanol. The physical characterization showed a significant amount of disorder in the carbon structure and the electrochemical characterization showed quasi‐reversible behavior without any electrode pretreatment. We then used unmodified graphene/PLA electrode to quantify Hg, and Pb and Cd in 0.01 M HCl and 0.1 M acetate buffer using square wave anodic stripping voltammetry. We were able to quantify Hg with a limit of detection (LOD) of 6.1 nM (1.2 ppb), but Pb and Cd did not present measurable peaks at concentrations below ～400 nM. We improved the LODs for Pb and Cd by depositing Bi microparticles on the graphene/PLA and, after optimization, achieved clear stripping peaks at the 20 nM level for both ions (4.1 and 2.2 ppb for Pb²⁺ and Cd²⁺, respectively). The results obtained for all three metals allowed quantification below the US Environmental Protection Agency action limits in drinking water.     

Click‐Conjugation of Nanogold‐Functionalized PAMAM Dendrimer: Toward a Novel Electrochemical Detection Platform

This work reports a new electrochemical monitoring platform for sensitive detection of Cu²⁺ coupling click chemistry with nanogold‐functionalized PAMAM dendrimer (AuNP‐PAMAM). The system involved an alkyne‐modified carbon electrode and an azide‐functionalized AuNP‐PAMAM. Initially, the added Cu²⁺ was reduced to Cu⁺ by the ascorbate, and then the azide‐modified AuNP‐PAMAM was covalently conjugated to the electrode via Cu⁺‐catalyzed azide‐alkyne click reaction. The carried AuNPs accompanying PAMAM dendrimer could be directly monitored by stripping voltammetry after acidic pretreatment. By introduction of high‐loading PAMAM dendrimer with gold nanoparticles, as low as 2.8 pM Cu²⁺ (ppt) could be detected, which was 125‐fold lower than that of gold nanoparticle‐based labeling strategy. The method exhibited high specificity toward target Cu²⁺ against other potentially interfering ions, and was applicable for monitoring Cu²⁺ in drinking water with satisfactory results.     

Solid-contact Cu(II) ion-selective electrode based on 1,2-di-(<Emphasis Type="Italic">o</Emphasis>-salicylaldiminophenylthio)ethane

The development of Cu(II) solid-contact ion-selective electrodes, based on 1,2-di-(o-salicylaldiminophenylthio)ethane as a neutral carrier, is presented. For the electrodes construction, unmodified carbon ink (type 1 electrode) and polymer membrane-modified carbon ink (type 2 electrode) were used as solid support and transducer layer. Also, carbon ink composite polymer membrane electrode (type 3 electrode) was prepared. The analytical performance of the electrodes was evaluated with potentiometry, while bulk and interfacial electrode features were provided with electrochemical impedance spectroscopy. It is shown that modification of carbon ink with polymer membrane cocktail decreases the bulk contact resistance of the transducer layer and polymer membrane, thus enhancing the analytical performance of the electrode in terms of sensitivity, linear range, and stability of potential. The optimized electrodes of types 2 and 3 exhibit a wide linear range with detection limits of 1.8 × 10⁻⁶ and 1.6 × 10⁻⁶ M, respectively. They are suitable for determination of Cu²⁺ in analytical measurements by direct potentiometry and in potentiometric titrations, within pH between 2.3 and 6.5. The electrodes are selective for Cu²⁺ over a large number of tested transition and heavy metal ions.     

A Sensitive Biosensor for Determination of Cu2+ by One‐step Electrodeposition

A simple one‐step electrodeposition method is described to fabricate three dimensional ordered macroporous chitosan?prussian blue?single walled carbon nanotubes (3DOM CS?PB?SWCNTs) film onto the gold electrode surface to fabricate a copper ions (Cu²⁺)‐specific DNAzyme biosensor. The new sensing strategy for sensitive and selective detection of Cu²⁺ was based on Au nanorods (AuNRs) as signal amplification labels. The electrochemical signal of glucose increased with the concentration of Cu²⁺ increasing. The morphologies and electrochemistry of the composites were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical techniques including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and so on. Linear correlations of copper ion concentration were obtained in the range from 10^?18 M to 10^?5 M, achieving with a limit of detection of 10^?19 M (S/N=3). Parameters affecting the biosensor response such as temperature, the cleavage time and the time of hybridization were optimized. This biosensor showed a wide range, low detection limit, good reproducibility and high stability. Additionally, these striking properties endow the biosensor with a great promise for analytical applications.